The final report on a serious in-flight electrical system failure in an Airbus A319 contains 14 recommendations for changes to equipment, engineering procedure and operational security,
En route from Alicante, Spain to Bristol, UK on 15 September 2006, the EasyJet aircraft (G-EZAC) suffered a loss of electrical power that left the captain with no flight instruments, and the aircraft with no autopilot or autothrottle and no means of communication for the remainder of the flight, according to the UK Air Accidents Investigation Branch report.
In addition, the loss of all transponder signals from G-EZAC for about 10min over north-west France deprived Brest air traffic control of its ability to track the aircraft, at the same time as rendering traffic alert and collision avoidance systems ineffective.
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The captain elected to continue the flight to its destination because he had good weather reports for Bristol and feared that divergence from the planned route with no communication might precipitate interception by military aircraft with potentially serious consequences because, with curtailed aircraft capabilities, he might not be able to comply with intercept signals.
The AAIB report says: "While in the cruise at flight level 320 (32,000ft/9,750m) in visual meteorological conditions, the aircraft suffered severe disruption of the electrical power system, causing multiple aircraft systems either to cease operating or to become degraded, significantly increasing the flightcrew's workload. All means of radio communications became inoperative and remained so because they all relied on a single busbar which de-energised and was unavailable for the remainder of the flight."
The causes of the incident, according to the AAIB, included "an intermittent fault in the No 1 generator control unit, which caused the loss of the left electrical network; an aircraft electrical system design which required manual reconfiguration of the electrical feed to the AC Essential busbar in the event of de‑energisation of the No 1 AC busbar, leading to the loss or degradation of multiple aircraft systems, until the electrical system is reconfigured; and the inability of the flightcrew to reconfigure the electrical system, for reasons which could not be established".
The aircraft had been dispatched from Alicante under a minimum equipment list provision despite the No 1 main generator being declared unserviceable on the inbound flight and not repaired. The left electrical system was powered by the auxiliary power unit generator.
The investigator remarked that, in this case, the aircraft was stable in the cruise in VMC conditions but the failure could equally have occurred in instrument meteorological conditions and at low level in a critical phase of flight.
For these and other reasons, says the AAIB, "the potential hazard of loss of the AC BUS 1, AC ESS and DC ESS busbars was more serious than the airworthiness authorities had assessed". The AAIB, after a previous A320 series electrical incident, recommended on 13 December 2006 that Airbus introduce a modification to automate the transfer of the electrical feed to the AC ESS busbar in the event of the loss of the AC BUS 1 busbar.
Airbus issued a service bulletin to enable this in 2007, and the AAIB's G-EZAC report has repeated the call for this change to be implemented.
The European Aviation Safety Agency has told the AAIB it will make this modification compulsory.
Included in additional recommendations are that EASA should require the modification of affected A320‑series aircraft so that the loss of a single busbar does not result in the complete loss of radio telephony communications; EASA should require Airbus to review the A320‑series master minimum equipment list provision that an aircraft may be dispatched with an integrated drive generator inoperative; Hamilton Sundstrand should modify its repair and overhaul procedures to ensure that a unit with an excessive service rejection rate or a recurrent fault is not repeatedly released back to service.
Finally, the AAIB recommends that, because of security concerns, EASA and the US Federal Aviation Administration should formally recategorise incidents involving total communications loss from "serious" to "hazardous".
Source: Flight International
